Abscisic acid (ABA) is a natural occurring hormone found in all higher plants (Cutler and Krochko. 1999. Trends in Plant Science. 4: 472-478.; Finkelstein and Rock. 2002. The Arabidopsis Book. ASPB, Monona, Md., 1-52). ABA is involved in many major events of plant growth and development including dormancy, germination, bud break, flowering, fruit set, growth and development, stress tolerance, ripening, abscission and senescence. One of the roles of ABA is the regulation of water relations in plants through the control of stomata opening and closure.
Most plants have improved drought tolerance following application of ABA, but plants differ in their sensitivity to applied ABA. Different types of ornamental plants differ in both the extent of increased drought tolerance and potential for undesirable side effects from ABA treatment. Others have reported ABA effects on transpiration of whole plants or excised plant parts and yellowing of excised plant parts. Foliar application of ABA reduced the transpiration of potted Poinsettia plants (Krizek, et al., 1986, Influence of soil moisture and ABA acid pretreatment in modifying SO2 sensitivity in poinsettia, J. Amer. Hort. Sci. 111:446-450). ABA applied through the petiole of excised Coleus leaves reduces their transpiration rate compared to excised leaves standing in water (Rajapakse, et al., 1988, Transpiration and water use of potted floricultural plants under low light conditions, J. Amer. Hort. Sci. 113:910-914). Treatment of Geranium cuttings causes the undesirable effect of leaf yellowing (Mutui et al., 2005, Journal of Horticultural Science & Biotechnology 80: 453-550). There are no previous reports that could be used to determine which ornamental plants benefit from ABA application in terms of reduced transpiration rates without unacceptable risk of ABA-induced leaf yellowing or abscission.